Chemical ionization procedure

Atmospheric-pressure ionization mass spectrometry (Horning et al., 1973 Carroll et ai, 1974) is a chemical ionization procedure that differs from the standard technique in a number of ways. The reaction chamber (ion source) is at atmospheric pressure and is external to the high-vacuum region of a quadrupole mass analyser. Ions and molecules enter the mass analyser region through a small aperture. The ions are obtained by ion lenses, while... 

Macerated plant material is homogenized with a mixture of methanol and 1.2N hydrochloric acid (HCl) in water (4 1, v/v) and then with methanol. An internal standard solution is added to the filtrate and the filtrate is adjusted to a constant volume. A portion of the filtrate is rotary evaporated to dryness and hexane is added to the extract before a Florisil cleanup procedure is performed. The extract is dissolved in toluene for analysis by GC/MS in the negative chemical ionization (NCI) mode. 

Olah, T.V., McLoughlin, D.A., and Gilbert, J.D. 1997. Simultaneous determination of mixtures of drug candidates by liquid chromatography/atmospheric pressure chemical ionization mass spectrometry as an in vivo drug screening procedure. Rapid Commun. Mass Spectrom. 11 17. 

Positive ions are usually generated in these techniques, as in mass spectrometry, by electron bombardment. Photo-ionization, laser desorption and chemical ionization have also been used for specific applications. When the ionizing energy is above the ionization potential of the parent compound, this procedure may result in the formation of several fragment ions. Collisions of parent and fragment ions with neutral molecules may then give rise to a sequence of chemical reactions. 

In recent years, several procedures have been developed for handling high molecular weight, water-soluble biomolecules. Several of these procedures are here briefly described. [See the Chapman (1993) and Watson (1985) references for a thorough discussion of these techniques. The Harrison (1992) reference presents a thorough treatment of chemical ionizations.]... 

A simple cleanup procedure based on acidic protein precipitation and LLE with ethyl acetate was used for the determination of OXA, CLO, and DICL in bovine muscle. The detection was accomplished with particle-beam MS with negative-ion chemical ionization, which was found more sensitive than electron-impact mode. Deviation from the linearity of response was observed, which could be caused by the phenomenon of coeluting carrying analyte particles through the particle beam (60). 

Conventional electron impact or chemical ionization mass spectrometry requires that volatilization precede ionization and this is clearly a limiting factor in the analysis of many biochemically significant compounds. A newer ionization technique, field desorption (FD) (1, 2 ) removes this requirement and makes it possible to obtain mass spectrometric information on thermally unstable or non-volatile organic compounds such as glycoconjugates and salts. This development is particularly significant for those concerned with the analysis of glycolipids and we have therefore explored the suitability of field desorption mass spectrometry (FDMS) for this class of compounds. We have evaluated experimental procedures in order to enhance the efficiency of the ionization process and to maximize the information content of spectra obtained by this technique. 

The emission of molecular ions in organic SIMS is discussed with respect to the method of ionization and the various sample preparation and matrix-assisted procedures used. The matrices include various solid-state and liquid matrices such as ammonium chloride, charcoal, glycerol, and galliun. A neutral beam source is described to analyze thick insulating films. Various chemical derivatization procedures have been developed to enhance the sensitivity of molecular SIMS and to selectively detect components in mixtures. 

Derivatization was conducted by the addition of a 10% H-ethyl-diiso-propylethylamine solution and a-bromo-2,3,4,5,6-pentafluorotoluene. Sample obtained from the derivatization procedure were dissolved in ethyl acetate prior to injection in splitless mode using a DB-1 capillary column. Helium was used as the mobile phase, and the injector temperature was set at 290 °C with a transfer line temperature of 270 °C. Sample detection used ion trap MS for detection, with the detector being set at negative chemical ionization with m/z = 262 (for CCA) and m/z = 286 (for the internal standard). The limit of quantitation was 5 ng/ml, and the average recovery ranged from 92.0% to 114%. In addition, the extraction efficiency ranged from 48.2% to 55.6% for concentrations of 5, 50, and 250 ng/ml. Samples were reported to be stable for up to 6 months when stored at 18 °C. 

G.C./M.S. results for pentazocine previously reported include both derivatization and nonder-ivatization procedures. Underivatized pentazocine gave a molecular ion at m/e 285 and the nor-ion at m/e 21 (32) while the 217 base peak and a 202 peak were observed by a multiple ion detector (33). Chemical ionization with methane gave a molecular ion of m/e 286 and fragments shown below (34). m/e... 

Even the lawn format still does not represent the final limit of miniaturization. The one well/one catalyst or one bead/one catalyst strategy, where catalyst identity is spatially coded, can be replaced by in situ synthesis combined with mass spectrometry [48]. The advantage of this strategy is the use of a mass spectrometer for the synthesis, reaction and analysis. The described electrospray ionization procedure helps to avoid the cleavage of chemical bonds, which would falsify the results. The synthesis step does not have to deliver clean and isolated products. Instead, after synthesis, the reactants are first separated by a quadrupole. In a second step, they are further reacted in an octapole and the reaction products are finally isolated in a second quadrupole and analyzed. Figure 3.15 describes the screening process in detail [49],... 

One of the major advantages of LC-MS/MS over GC-MS or GC-MS/MS is that steroid hormones may be analyzed directly by LC-MS/MS without derivatization procedures, which are time-consuming and tedious [22,50-53], However, a number of studies demonstrated that the chemically derivatized steroid hormones were significantly more sensitive to LC-MS/MS detection than the underivatized hormones, because the neutral molecules of estrogens and metabolites might not be effectively ionized under electrospray ionization (ESI) or atmospheric pressure chemical ionization (APCI) modes [4, 21, 25, 54, 55], In order to enhance the steroid hormone molecules sensitivity for LC-MS/MS analysis at pg/mL level, chemical derivatization is an effective technique for analysis of steroid hormones and metabolites. A list of derivatization reagents and application examples for steroid hormone analyses by LC-MS/MS and GC-MS are presented in Table 3. 

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